Twin roll mounting for cross roll straightening machines



Nov. 14, 1961 o. J. SKAWDEN ETAL 3,008,510

'rwm ROLL MOUNTING FOR CROSS ROLL STRAIGHTENING MACHINES Filed May 27, 1958 6 Sheets-Sheet 1 Fig. 1

ATTODNEYS 1961 o. J. SKAWDEN ETALY 3,008,510

TWIN ROLL MOUNTING FOR CROSS ROLL STRAIGHTENING MACHINES Filed May 27, 1958 6 Sheets-Sheet 2 M INVENTORS 000 J \SX IWDEIV 67% M fad/N50 BY rm a I ATTORNEYS Nov. 14, 1961 o. J. SKAWDEN ETAL 3,008,510

TWIN ROLL MOUNTING FOR. CROSS ROLL STRAIGHTENING MACHINES Filed May 27, 1958 6 Sheets-Sheet 3 INVENTORS 000 J. SAdWDE/V JYAQU/VMWBl/VJUN A6103 I BY Nov. 14, 1961 O. J. SKAWDEN ETAL TWIN ROLL MOUNTING FOR CROSS ROLL STRAIGHTENING MACHINES Filed May 27, 1958 6 Sheets-Sheet 4 INVENTORS IITGEAEKF Nov. 14, 1961 o. J. SKAWDEN El'AL 3,008,510

TWIN ROLL MOUNTING FOR CROSS ROLL STRAIGHTENING MACHINES Filed May 27, 1958 6 Sheets-Sheet 5 lll Q EIIHHHB INVENTORS 000 J. Min MW P25. 6 arm/v 4/. MIA 50V Nov. 14, 1961 o, J, s w ET AL 3,008,510

TWIN ROLL MOUNTING FOR CROSS ROLL STRAIGHTENING MACHINES 6 Sheets-Sheet 6 Filed May 27, 1958 ATMR/VEYS United States Patent Ofifice 3,008,510 Patented Nov. 14, 196I vania V p Filed May 27,1958, ser. No. 738,165 16 Claims. (Cl. 153-405) This invention relates to a twin roll mounting for cross roll straightening machines used to straighten round stock. I A cross roll straightener of the above type that is in common use has a pair of opposed rolls at each end of the machine and a single unopposed deflecting roll mounted between the end pairs. Straightening is accomplished by bending the stock, usually in the form of a tube or bar, between the deflecting roll and the end pairs of rolls and by the action of the rolls themselves. The bending of the tube and the contact pressure of the individual rolls thereon tend to deform the tube into an oval shape and, since the tube itself is rotated rapidly by the rolls as it passes through the straightener, the ovaling or flexing of the tube wall causes considerable cold Working of the metal throughout the entire circumference of the tube. The residual stresses induced by such cold working are generally undesirable. They tend to make the straightened tube more susceptible to collapse from external pressure than a tube that has not been straightened; and this result is particularly noticeable in straightening tubes having a large ratio of external diameter to wall thickness. Accordingly, where it is desired that the straightened tube have a high resistance to collapse, as, for example, where the tube is to be used for oil well casing, it is important that the residual stresses in the tube be kept at a minimum. Likewise, it is desirable to keep these stresses at a minimum when straightening soft metal tubing of large diameter and thin wall section to avoid permanent deformation of the tube and marring of its surface.

These undesirable stresses can be materially reduced by increasing the number of rolls around a given section of the tube to provide spaced multiple contacts between the tube and rolls that will limit the amount of ovaling deformation and by keeping individual roll pressures on the tube at a minimum. The straightener referred to in the preceding paragraph, with its opposed rolls, has a maximum ovaling effect and the individual roll pressures are high. The ovaling effect can be reduced by replacing each pair of opposed rolls with a cluster of three equally spaced rolls, as shown, for example, in Patent No. 2,556,120, issued to the assignee of the instant application. Such a cluster provides greater multiple contacts between the rolls and the stock, with less ovaling effect than is provided by two opposed rolls; but, due to the equal spacing of the rolls around the periphery of the stock, the roll pressures are substantially unchanged from those present in a pair of opposed rolls. Roll pressures can be reduced, and 'ovaling deformation lessened still further, by using clusters of four equally spaced rolls, as shown in Patent No. 2,411,395; also assigned to the assignee of the instant application. However, straighteners of this type, in which two adjacent rolls are spaced around the axis of the stock at a fixed angle of 90 cannot accommodate the lower limit of stock sizes without roll interference that can be accommodated by the same two rolls when spaced at a greater angle. Thus, rolls spaced apart by 90" cannot handle stock of as small diameter as can the same rolls when spaced apart by 120, and two rolls 60 apart cannot handle stock of as small diameter as can be handled by those rolls when 90 apart. Accordingly, while roll pressures are reduced by de- 2 creasing the angular spacing between two adjacent rolls about the axis of the stock, so long as that angular spacing is substantially fixed for all stock sizes, the capacity of the rolls to handle small diameter stock will be reduced in proportion. I

The present invention is directed to providing a twin cross roll mounting that can be used to replace a single unopposed roll, or one or both of two opposed rolls, in a straightening machine; that will permit adjustment of the angular spacing of two adjacent rolls about the axis of the stock to obtain the optimum angle for rolls of a given size for each particular size of stock over a wide range of stock sizes, thereby reducing roll pressures to a minimum, particularly for large diameter stock; and that will permit the skew of the roll axes to be varied automatically in response to the angular adjustment of the rolls to accommodate different sizes of stock.

Still other objects will be apparent from the following description of a preferred embodiment of the invention in connection with the accompanying drawings, in which FIG. 1 is a front elevation of a straightening machine embodying this invention;

FIG. 2 is an end elevation of the machine in FIG. 1;

FIG. 3 is an enlarged view of the twin roll mounting shown in FIG. 2, with the rolls positioned for straightening small diameter stock;

FIG. 4 is similar to FIG. 3, except that the rolls are positioned for straightening large diameter stock;

FIG. 5 is an enlarged partial section along the line VV of FIG. 4;

FIGS. 6 and 7 are sections along the line VI-VI of FIG. 5, with the roll assemblies in the positions shown in FIGS. 3 and 4, respectively;

FIG. 8 shows diagrammatic sections of the twin rolls engaging stock of dilferent diameters to illustrate how the cradle axes of the roll assemblies are determined under particular conditions;

FIG. 9 is an elevation, partly in section, of a modified twin roll mounting, showing alternative means for automatically adjusting the skew of the roll axes;

FIG. 10 is a plan view, partly in section, of the modification of FIG. 9; v

FIG. 11 is a partial rear elevation of the modification of FIG. 9; and

FIGS. 12-15 are schematic diagrams showing the relation of the angle between the thrust planes of the rolls in a twin roll assembly to the diameter of the stock being straightened, for twin rolls of a given representative size. In the examples of prior art straighteners, referred to above, two adjacent rolls, spaced apart by or less, are maintained in proper contact with stock of different sizes primarily by varying the distance between the rolls, the angular disposition of the rolls about the axis of the stock being kept essentially constant. According to the present invention, on the other hand, two adjacent rolls are maintained in proper contact with stock of different sizes primarily by varying the angular disposition of the rolls about the axis of the stock. the rolls preferably being kept as close together as practicable at all times to reduce the individual roll pressure for a given set of rolls.

The twin cross roll mounting of this invention broadly includes a cradle frame supported on the main frame of the straightener and provided with a bearing surface (or surfaces) of revolution 7 about a cradle axis (or axes) substantially parallel to the axis of the stock, i.e., to the pass line of the straightener. Rotatably supportedon this bearing surface (or surfaces) are two roll assemb1ie s,each containing a single cross roll. Each roll assembly has a thrust axis defined by the straight line passing through the center of the gorge circle of the cross roll and intersecting the pass line at substantially right angles. As will be explained more fully below, this thrust axis must also be substantially perpendicular to the roll axis in each roll assembly in order to maintain proper contact between the roll and the stock. Each roll assembly also has a thrust plane defined by its thrust axis and the pass line. The cradle axis, about which each roll assembly can be rotated, is so determined that the dihedral angle between the thrust planes of the two roll assemblies can be varied inversely with the outside diameter of the stock being straightened. In this way, it is possible to maintain the minimum practicable clearance between the twin cross rolls, so that the pressure exerted by each is kept at a minimum over a wide range of stock sizes, and particularly for stock of large diameters.

A specific embodiment of this invention is shown in FIGS. 1-7. There are two separate cradle bearing surfaces on the cradle frame, each surface having the same radius but a different axis of revolution. These cradle axes are each substantially parallel to the pass line, and each lies in the thrust plane of its roll assembly. Each roll assembly includes a bearing block, a roll bracket, and a cross roll. The bearing block is slidably mounted on one of the bearing surfaces of the cradle frame so that the whole assembly can be rotated about its cradle axis. The roll bracket is pivotally mounted on the bearing block for rotation about the thrust axis. The cross roll is mounted on the roll bracket for rotation about the roll axis, which intersects the thrust axis at substantially right angles. Means are provided for angularly adjusting each roll assembly about its cradle axis, which varies the dihedral angle between the thrust planes of the two as semblies. In addition, means are provided for angularly ajusting the axis of each roll about the thrust axis of its roll assembly to adjust the skew of the rolls for proper contact between the rolls and dilferent sizes of stock.

Referring to the drawings, FIGS. 1 and 2 show elevations of a straightening machine having two large rolls in the lower bank and three smaller twin roll assemblies in the upper bank, the center twin roll assembly acting as deflecting rolls. Other combinations and arrangements of single rolls and twin rolls, or of twin rolls alone, will be obvious, the arrangement shown having been chosen for its relative simplicity.

Since the general construction of the straightener forms no part of this invention, and since each of the twin roll mountings are essentially identical in structure and operation, it will sufiice to describe only one of those mountings fully, for example, that shown in FIG. 2, and in enlarged detail in FIGS. 3-7. The frame 1 of the straightener supports a cradle frame 2, which can be raised or lowered in the main frame by the usual screwdown 3 to take care of stock of different diameters and to apply the desired pressure to the stock. The lower part of the cradle frame 2 is bifurcated to provide an open space or slot 4 between the cradle walls 6 and 7 (see FIG. Secured to the bottoms of those walls are two spaced bearing shoes 8 and 9, which are segments of hollow cylinders (see FIGS. 6 and 7). The bottoms of those shoes form two spaced concave bearing surfaces 11 and 12, respectively, each of which is generated by a straight line, with the same radius of revolution, about different axes of revolution, herein called cradle axes. Those axes are substantially parallel to the pass line 0, which coincides substantially with the longitudinal axis of that portion of the stock S that is properly incontact with the twin rolls during the straightening operation. The cradle axes according are substantially normal to the plane of the paper (in FIGS. 3-4, 6-7) and intersect that plane at points A and B. I

Rotatably mounted on the cradle bearing surfaces 11 and 12, respectively, are separate roll assemblies X and Y, each of which includes a bearing block 16, a roll bracket 17, and a cross roll 18. The bearing block 16 has a convex surface conforming to and engaging thebearing surface 11 or 12 of the cradle frame 2 but sliding movement of the bearing blockthereon is confined by guides 19 (see FIG. 5) to rotationof the block about one of the cradle axes at A or B. These guides are secured to the sides of the bearing block and embrace the bottom outside edges 21 and 22 of walls 6 and 7, respectively, of the cradle frame. The roll bracket 17 is pivotally mounted on the bearing block 16 by a pivot pin 23, which passes through the bearing block and through a circumferential slot 24 in one of the bearing shoes, 8 or 9, of the cradle frame. The outer end 26 of this pin extends into the open space 4 between the walls 6 and 7 and is secured by a nut 27, and by a compression spring 28 disposed between the nut and a washer 29 contacting the inner surface of the shoe. Preferably, but not necessarily, a backing plate 31 is mounted between bracket 17 and bearing block 16 and secured to the former by bolts 32 extending through elongated, arcuate slots 33 (shown only in section in FIGS. 6 and 7), so that the roll bracket 17 and the backing plate 31 may be angularly adjusted relative to each other when desired.

On each of the roll brackets 17 is mounted a cross roll 18 of conventional type, having a concave contoured surface that provides substantially line contact with the stock being straightened. A straight line 34 extending through the roll center 36 (i.e., the center of the gorge circle, which is the right circular section at the least diameter of the roll) and intersecting the pass line 0 at right angles, defines the thrust axis, as that term is used herein, of each roll assembly. The thrust plane of each roll assembly is the plane defined by its thrust axis and the pass line.

The location of the cradle axes, about which the roll assemblies rotate, is largely determined by the geometry peculiar to skewed contoured rolls and requires substantial fulfillment of the following conditions: (1) the thrust axis of each roll assembly must be substantially perpendicular to the axis of the cross roll in that assembly, (2) to maintain minimum roll clearance between the twin rolls for all sizes of stock being straightened, the roll centers must be slightly farther apart when straightening large as compared to small diameter stock; and (3) the dihedral angle between the thrust planes of the two roll assemblies must vary inversely with the outside diameter of the stock being straightened.

The above conditions will be explained in connection with FIGS. 6 and 7, showing the different angular positions of the two roll assemblies for properly contacting large and small diameter stock, respectively, in accordance with this invention. Due to the deviation of the roll contour from cylindrical form and also due to the skew of the roll axes 35 (see FIG. 5) about the roll bracket axes (the axes of pivot pins 23, which coincide in this embodiment with the thrust axes 34) the roll sections shown in FIGS. 6 and 7 are approximately'elliptical, and for convenience will be referred to herein as being elliptical. For proper contact between each roll and the stock being straightened (regardless of the size of the stock), the stock must be substantially tangent to the roll at least at a point 37 (FIGS. 6 and 7) on its gorge circle, which is the circumference of the right circular section of the roll through the roll center 36. For this to be true for all angles of skew and all stock sizes it is obvious that the thrust axis of each roll assembly must be substantially perpendicular to the axis of the cross roll in that assembly; and axiomatically, in FIGS. 6 and 7, the major axis 38 of the elliptical section must lie on the projection of the roll axis 35, the minor axis must be a diameter of the gorge circle, and this diameter must coincide with the thrust axis 34. I

To maintain minimum roll pressures for various sizes of stock, the centers 36 of the twin rolls should be kept as close together as practicable, which means that the di hedral angle between their thrust planes (in the embodiment shown, this equals the included angle between their thrust axes) will vary inversely with the stock diameter. This condition is fulfilled in the twin roll mounting shown, where the angle [3 in FIG. 7 (large diameter stock) is smaller than angle 55 in FIG. 6 (small diameter stock).

, Another condition of proper contact between rolls and stock is that the skew angle of the roll axes relative to the pass line increases slightly as the stock diameter increases, e.g., the skew angle of the rolls in FIG. 7 is slightly larger than in FIG. 6. This is accomplished by rotating the roll brackets about the roll bracket axes (in this embodiment, the same as the thrust axes). An increase in the skew angle of each roll increases slightly the length of the major axes of all the elliptical roll "sections (in planes perpendicular to the pass line); and, more important, these major axes rotate about the cradle axes (when the dihedral angle between the roll assemblies decreases to accommodate larger sizes of stock) in a direction that tends to cause roll interference. Accordingly, the roll centers 36 must be slightly farther apart when straightening large diameter stock (FIG. 7) as compared to small diameter stock (FIG. 6), in order to keep minimum clearance between the rolls for all size ranges of stock being straightened.

It will be seen that the foregoing conditions are fulfilled in FIGS. 6 and 7 by having the cradle axes parallel to the pass line and intersecting the plane of the paper at points A and B. Rotation of the roll assemblies about those axes will necessarily maintain the required perpendicularity between the thrust axes and the roll axes. Since the thrust axes in this particular structure lie in the same plane, the dihedral angle between the thrust planes is the same as the included angles between the thrust axes, and is smaller in FIG. 7 (where the stock diameter is large) than in FIG. 6 (where the stock diameter is small). The cradle axes lie between the roll centers 36 and the cradle frame 2, so that as the angle between the thrust axes decreases (as the stock diameter increases), the roll centers are moved further apart to provide necessary minimum clearance. It is also possible, by using procedures similar to those referred to below in connection with FIG. 8, to design twin rolls of a certain size so that the cradle axes of the twin roll assemblies will coincide.

Means are provided for simultaneously rotating both roll assemblies about their respective cradle axes. In each roll assembly, an arm 41 passes through a slot 42 (which is a continuation of slot 24 beyond the shoulder 43, but wider than slot 24) in the bearing shoe 8 or 9, with one end of the arm rigidly secured to the bearing block 16 and the other end pivotally secured by pin 44 to an internally threaded block 45. This block is threaded on an adjusting screw 46, rotatably mounted in the cradle frame 2 and slidable vertically therein (note clearance spaces 47 adjacent screw retaining collars 48) to take care of arcuate movement of the blocks 45 about the cradle axes. The screw may be turned by any suitable means, such as a handwheel 49. Screw 46 is provided with left and right hand threaded portions 46a and 46b, respectively, so that rotation of the handwheel will cause each roll assembly to rotate an equal amount about its cradle axis, A or B.

FIGS. 3 and 4 show toggle linkage means for automatically adjusting the skew of the roll in roll assembly X whenever the angular disposition of the roll assemblies is changed, as described, above for stock of different diameters (a similar means is provided for the roll assembly Y, but is positioned on the other side of the cradle frame 2 and is not shown in the drawings). A main link 51 is pivoted at one end to the cradle frame 2 and at its other end to the end of links 53 and 54. Link 53 has its outer end pivoted to the backing plate 31, and link 54 has its outer end pivoted to the bearing block 16. The length of each of the three links can be adjusted within limits by threaded couplings 56. This linkage system rotates the roll brackets about the roll bracket axes (thrust axes) of the roll assemblies whenever their angular disposition is changed by turning the handwheel 47. FIG. 4 shows the approximate position of the linkage when the cross rolls engage stock of large diameter, while FIG. 3 shows their approximate position when the cross rolls engage (with less skew) stock of small diameter. In case it is desired r 6 to adjust the skew position of a roll independently of the linkage system, as in setting up the straightener, this 'may be done by loosening bolts 32 and adjusting the angle of the roll bracket 17 relative to the backing plate 3-1.

In FIGS. 9-11 are shown alternative means for rotating each roll assembly about its cradle axis and at the same time automatically adjusting the skew of the rolls to the proper angle for contacting stock of different sizes. Each assembly is provided with an extensible composite arm passing through the slot '42 in the bearing shoe, and including a U-shaped pin member 61 and a socket member 62. From the bottom of the U-shaped member 61 exten'ds a heavy 'pin 63, which is slidably and rotatably received within a hole in the socket member 62. The latter is secured to the backing plate 31 of the roll assembly. The ears 64 of the U-shaped member are pivoted to a threaded block 66 on an adjusting screw 67, similar to the adjusting screw 46 previously described, except that the screw 67 is skewed in a horizontal plane, as shown in FIG. 10. This screw is provided with right and left hand threaded portions 67a and 67b, respectively, and is supported in the cradle frame 2 by an eccentric mounting, as shown in FIGS. 10 and l l, for making minute adjustments in the angularity of the screw relative to the pass line. The mounting includes a circular plate 70, provided with numerous bolt holes 71 around its circumference, and is secured to the cradle frame at two fixed points by bolts 72. The adjusting screw 67 is supported eccentrically in this plate by spherical bearings 73, slidably mounted on unthreaded portions of the screw, and axial movement is limited by adjustable collars 74. By rotating the mounting plates at each end of the screw in opposite directions, after removing the bolts 72, and then rebolting the plates to the cradle frame, the screw can be kept horizontal, while its angularity relative to the pass line is changed within desired limits fixed by the eccentricity of the screw mounting. It will be clear from FIGS. 9-11 that the skew angle of the rolls will be changed automatically as the roll assemblies are rotated about their cradle axes by means of the adjusting screw 67, and that each arm will permit rotation of its pin member relative to its socket member, as well as movement of those two members towards and away from one another. This latter'feature permits the threaded blocks 66 to move in a straight line on the screw, while the blocks are rotated about the cradle axes of the roll assemblies. Of course, if it is desired to adjust the skew of a roll independently of the automatic means, that maybe done by loosening the bolts 32 securing the roll bracket 17 to the backing plate 31, as previously described.

It will be clear from the foregoing description in connection with FIGS. 3-7 and 9-11 that, in adjusting the twin roll assemblies for different sizes of stock, the rolls are rotated (1) about their cradle axes and (2) about their roll bracket axes. These two motions can be obtained through only one pair of engaging surfaces, by providing spherical bearing surfaces on the cradle frame 2 (and bearing blocks 16) instead of the cylindrical surfaces shown in the drawings. The cradle centers of the spherical surfaces would be determined by procedures similar to those described in determining the cradle axes of the roll assemblies and would lie on those axes. With pin 23 extending through slot 24, rocking of the whole assembly about the cradle center of the spherical surface will be limited to a plane perpendicular to the pass line. Guide plates 19 would then be eliminated to permit bearing block 16 (which may now be integral with backing plate 31) to rotate on the spherical bearing surface about the axis of pin 23 for varying the skew of the roll. As an alternative construction, the guide plates 19 could be retained but secured to the bearing frame 2 (instead of the bearing block 16), and the bearing block made with a cylindrical surface engaging the inner side of the guide plates to permit its rotation about pin 23. j

The straightener shown in FIGS. 1 and 2 is adapted to maintain the bottom of the stock, regardless of its diameter, at substantially the same pass level, i.e., tangent to a horizontal plane that its substantially fixed. This can be accomplished without vertcial adjustment of the single rolls 80 that are opposed to the twin rolls, because the cradle frame 2 supporting the twin roll mountings is vertically adjustable by means of the usual screwdowns to vary the spacing between the twin rolls and their opposed single rolls for stock of different diameters. Such a substantially constant pass level for the stock is a convenient feature, not only because it simplifies the mountings of the opposed single rolls 80 (which need only to be rotatable about their roll bracket axes), but also because auxiliary equipment, such as feed and delivery tables, can be maintained at the same height. If twin roll mountings are used, as they may be, in the lower bank of rolls (opposed either to single rolls or to twin roll mountings in the upper bank), they can be identical in structure to the twin roll mounting already described; but then the pass level cannot be maintained substantially constant for different sizes of stock, unless the lower twin roll mountings are provided with auxiliary vertical adjustment means. However, with a change in the location of the cradle axes of the lower twin roll mountings, they can accommodate different sizes of stock at substantially the same pass level without being vertically adjustable.

Such a modification in the location of the cradle axes is illustrated diagrammatically in FIG. 8, showing the relative positions of the roll sections in a plane perpendicular to the pass line for two different sizes of stock. Stock 81 (of small diameter) and the roll sections associated with it are shown in broken lines; stock 82 (of larger diameter) and its associated roll sections are shown in solid lines. Both sizes of stock are shown as tangent to a common plane at point 83, i.e., the pass level is the same in both cases. The rolls in contact with the small size stock 81 have their centers at points C and D, and their thrust axes CE and DE are perpendicular to the major axes 84 of the elliptical roll sections (broken lines). When the roll assemblies are rotated about their cradle axes to properly engage the large size stock 82, the roll centers are at points F and G, and the new thrus taxes FH and GH are again perpendicular to the major axes 86 of the second pair of elliptical roll sections (solid lines). Accordingly, the roll centers (and consequently each roll assembly) must rotate about cradle axes that will move the roll centers from positions C and D to positions F and G, with the left hand roll assembly rotating counterclockwise and the right hand roll assembly rotating clockwise (looking at FIG. 8). While not so shown in FIG. 8, the major axes 86 of the roll sections (solid lines) engaging the larger diameter stock 82 will be slightly longer than the axes 84 of the roll sections (broken lines) engaging the smaller diameter stock 81, due to the slightly greater skew of the roll axes in the former cases. For this reason, but primarily because of the direction of rotation of these axes about centers P and Q, the roll centers F and G are slightly farther apart (distance T than are the centers C and D (distance T to provide the necessary clearance between the rolls ot avoid roll interference, as previously described. The angle ,3, through which each roll center rotates is equal to one half the difference between angles 18,, and [3 These conditions determine the points P and Q, representing the intersection of the cradle axes of the left and right hand roll assemblies, respectively, with the plane of the paper, these cradle axes being substantially parallel to the pass line. Therefore, the cradle bearing surface of the right hand roll assembly will be a surface of revolution generated around its cradle axis, and is represented in the drawing by an are 87 about P as a center. Similarly, the cradle bearing surface of the right hand roll assembly will be a surface of revolution generated around its cradle axis, and is represented in the drawing by an are 88 about Q as a center.

The foregoing design may be embodied in a straightener. f example, in a four roll pass consisting of an upper twin roll mounting constructed in accordance with FIGS. 1-7 and an opposed lower twin roll mounting of the same basic structure, except that the bearing surfaces of the lower cradle frame will be generated about cradle axes, such as P and Q in FIG. 8, that do not lie in the thrust planes of their associated roll assemblies. Stock of different sizes may be put through such a pass at substantially the same pass level, without means for raising and lowering the lower cradle frame.

Under certain circumstances, it may be desirable to pivot the roll brackets eccentrically, i.e., the roll bracket axes instead of coinciding with the thrust axes will be parallel to them and displaced to the right or left in FIG. 5, so that they will be out of the plane of the paper in FIGS. 6 and 7. structurally, the roll assemblies will be the same as has been described, except for the displacement of the pivot pins 23. In such cases, and even in cases when the roll axes are not eccentrieally mounted, the thrust axes will not necessarily intersect the pass line at the same point (i.e., the roll centers may be staggered relative to the plane of the paper), and the dihedral angle between the thrust planes Will be one of the determining conditions in the location of the cradle axes, which may be ascertained by procedures similar to those described in connection with FIG. 8.

A straightener embodying this invention may contain various combinations of twin roll mountings and single rolls or of twin roll mountings. alone. It is a general purpose of this invention to provide a twin roll mounting that may be substituted for any one or more of the single opposed or unopposed rolls in a straightener, and the rolls may all be driven, or partly driven and partly idler rolls, as desired. It will also be understood that the rolls (whether twin rolls or single rolls) may be disposed laterally of, or at some other angle to, the pass line rather than above and below that line as shown in the drawings.

In FIGS. 12-15 are shown diagrammatically and ap proximately the proportionate variations in the halfangle between the thrust planes of a representative twin roll mounting having cross rolls of a given diameter when straightening stock of various sizes. The figures also show the roll load (or pressure) along the thrust axis of each roll assembly as a proportion of what the total load would be on a single roll positioned midway between the twin rolls and replacing those rolls. It will be noted that for the largest diameter stock (FIG. 15), the half-angle between the thrust planes is anly about 30 and that the pressure exerted by each roll is only about 58% of the pressure that would be exerted by such a single roll. Even with the smallest diameter stock shown (FIG. 12), the half-angle is around 482 and the component of force along the thrust axes is only about 75% of what would be exerted by such a single roll. Accordingly, the twin roll mounting will produce smaller stresses in the wall of tubing being straightened than can be obtained in conventional straighteners, and this result is paiticularly true where the twin roll mounting is either unopposed or opposed by another twin roll mounting. In addition, twin roll mountings, particularly when opposed to each other, provide multiple line contacts between the rolls and the stock that are spaced around the circumference of the stock, thereby limiting the ovaling deformation that can be imparted to the stock. The importance of limiting roll pressure and ovaling deformation have already been noted when straightening certain type of tubing, especially those having a large diameter and a relatively thin wall. In addition, the twin roll mounting will accommodate a greater range of smaller stock sizes for rolls of a given diameter than will conventional mountings of two adjacent rolls having a constant dihedral angle between their thrust planes.

According to the provisions of the patent statutes, we have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. A twin cross roll mounting for use in a straightening machine for straightening lengths. of round stock of various diameters Within a given range of diameters, in which the longitudinal axis of each length of stock substantially defines a pass line, said mounting comprising two separate cross roll assemblies each of which includes a separate skewed cross roll adapted to contact the stock being straightened, each roll assembly having a thrust axis defined by the line passing through the center of the cross roll in that assembly and intersecting both the pass line and the axis of that cross roll substantially at right angles and also having a thrust plane defined by its thrust axis and the pass line, and a cradle frame supporting each roll assembly for rotation about a defined cradle axis that is substantially parallel to the pass line and is located on the same side of the pass line as the line connecting the centers of the cross rolls when those rolls contact stock of the smallest diameter within the given range of stock diameters, whereby the dihedral angle between the thrust planes will vary inversely with the outside diameters of the stock when straightening stock of different sizes within the given range of stock diameters.

2. Apparatus according to claim 1, in which the cradle axis of each roll assembly is located on the opposite side from the pass line of a line connecting the centers of the cross rolls when those rolls contact stock of an extreme diameter within the given range of stock diameters, whereby the distance between the centers of the cross rolls will increase slightly as. the dihedral angle between the thrust planes decreases to provide minimum clearance between the rolls for all sizes of stock being straightened within the given range of stock diameters.

3. Apparatus according to claim 2, in which the cradle axis of each roll assembly intersects the plane of the gorge circle of the cross. roll in that assembly at a point within the locus of the gorge circle as determined by all sizes of stock being straightened within the given range of stock diameters.

4. Apparatus according to claim 1, in which the cradle axis of each roll assembly lies substantially in the thrust plane of that assembly.

5. Apparatus according to claim 4, in which the cradle axis intersects the thrust axis of that assembly between the center of the cross roll and the cradle frame.

6. Apparatus according to claim 1, in which the cradle axis of each roll assembly lies substantially in the thrust plane of that assembly and intersects the thrust axis of that assembly on the opposite side from the pass line of the center of the cross roll and within the confines of the locus of the gorge circle of that roll as determined by all sizes of stock being straightened within the given range of stock diameters.

7. Apparatus according to claim 1, in which each roll assembly includes a bearing block, a roll bracket, the bearing block having a convex bearing surface conforming to and slidably engaging a concave bearing surface on the cradle frame and the roll bracket being pivotally mounted on the bearing block and rotatably supporting the cross roll.

8. Apparatus according to claim 7, in which each roll assembly is angularly adjusted about its cradle axis. by an arm having one end secured to the bearing block of that assembly and its other end pivotally connected to and movable by a block threaded on an adjusting screw that is rotatably mounted on the cradle frame.

9. Apparatus according to claim 8, that includes automatic means for changing the skew of the roll in each roll assembly in accordance with the angular disposition of that assembly about its cradle axis, said means including a toggle linkage having a main link pivoted at one end to an end of each of two auxiliary links, the other end of the main link being pivoted on the cradle frame and the other ends of the two auxiliary links being pivoted, respectively, to the bearing block and the roll bracket.

10. Apparatus according to claim 7, that includes automatic means for simultaneously changing both the skew of the cross rolls and the angular disposition of the roll assemblies about their cradle axes, said means including a separate composite adjusting arm for each roll assembly, each arm having two members that are rotatable and extensible relative to each other, one of said members being fixed to the roll bracket and the other of said members being pivotally mounted on a block threaded on a single adjusting screw mounted at an acute angle to the pass line, the adjusting screw being provided with right and left hand threaded portions for controlling, respectively, the movement of the adjusting arm of each roll assembly, whereby rotation of the screw will simultaneously change the angular disposition of the roll assemblies about their cradle axes and at the same time change the angular disposition of the roll axes about their pivot pins so that the rolls may properly contact stock of different outside diameters.

11. Apparatus according to claim 10, in which the adjusting screw is adjustably mounted on the cradle frame for varying the acute angle of said screw relative to the pass line.

12. Apparatus according to claim 7, in which one of the members of the composite adjusting arm is provided with a cylindrical pin and the other of said members is provided with a cylindrical hole therein for slidably and rotatably receiving said pin.

13. Apparatus according to claim 1, in which the cradle frame has bifurcated portions defining an open space therebetween, two spaced bearing shoes rigidly secured to said portions and acting as a partial closure for said open space, each bearing shoe having a concave hearing surface representing a surface of revolution about a separate cradle axis, a separate roll assembly slidably mounted on each bearing surface for rotation about the cradle axis of that surface, each roll assembly including a bearing block and a roll bracket and a cross roll, the bearing b-lock having a convex bearing surface conforming to and slidably engaging the bearing surface of the bearing shoe, the roll bracket being pivotally mounted on the bearing block, the cross roll being rotatably mounted on the roll bracket, and means for angularly adjusting each roll assembly in the cradle frame about its cradle axis.

14. Apparatus according to claim 13, in which the roll bracket is pivotally mounted on the bearing block by [a pivot pin passing through the bearing block and through an arcuate slot in the bearing shoe so that a portion of said pin will extend into the open space within the cradle frame, the pivot pin being secured to the hearing shoe by a compression spring interposed between a bearing washer and an adjustable stop on the end of the pivot pin, and the bearing washer slidably engaging the surface of the bearing shoe opposite said bearing surface.

15. Apparatus according to claim 13, in which the cradle axis of each roll assembly is located on the opposite side from the pass line of a line connecting the centers of the cross rolls when those rolls contact stock of an extreme diameter within the given range of stock diameters and in which the cradle axis also intersects the plane of the gorge circle of the cross roll in that assembly at a point Within the locus of said gorge circle as determined by all sizes of stock being straightened within the given range of stock diameters.

16. Apparatus according to claim 1, in which the cradle axis of each roll assembly intersects the plane of the gorge circle of the cross roll in that assembly at a point Within the locus of said gorge circle as determined 1 1 by all sizes of stock being straightened Within the given 2,556,120 range of stock diameters.

References Cited in the file of this patent 508 210 UNITED STATES PATENTS 5 4 7:114

1,771,681 Kahn July 29, 1930 2,455,391 Sutton Dec. 7, 1948 12 Sutton June 5, 1951 FOREIGN PATENTS Ger-many Sept. 25, 1930 Canada Sept. 18, 1951 UNITED STATES P ATENT OFFICE CERTIFICATE OF CORRECTION.

Patent No. 3 )08,5lO November l4 1961 Gold J. Skawden et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 29 for the claim reference numeral ".7"

Signed and sealed this 10th day of, April l962 S EA L) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

